Paper feed apparatus

ABSTRACT

A paper feed apparatus comprises primary paper feed device  3  sequentially transferring only an uppermost print sheet P on a paper feed tray, and secondary paper feed device  4  guiding a tip end of the print sheet P transferred by the primary paper feed device  3  by a pair of guide members  12  and  13 , introducing the print sheet P to a portion between a pair of secondary paper feed rollers  10  and transferring the print sheet P introduced to the portion between the pair of secondary paper feed rollers  10  to a transport downstream side according to rotation of the pair of secondary paper feed rollers  10 . The paper feed apparatus is provided with a guide distance adjustment device  14  for making a distance between the pair of guide members  12  and  13  variable. The guide distance adjustment device  14  rotates eccentric cams  22  by rotation of an operation member  20 . A position of the upper guide member  12  is vertically changed to follow up lower surface positions of the eccentric cams  22 , thereby making the distance between the pair of guide members  12  and  13  variable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paper feed apparatus for sequentiallytransferring only an uppermost sheet out of sheets mounted on a paperfeed tray in a stacked state at predetermined timing.

2. Description of the Related Art

There is proposed a paper feed apparatus of such a type as shown in FIG.1. FIG. 1 is a schematic side elevational view of the proposed paperfeed apparatus. A paper feed apparatus 100 includes a paper feed tray102 for mounting many sheets 101 in a stacked state, primary paper feeddevice 103 for transferring only the uppermost sheet 101 on the paperfeed tray 102, and secondary paper feed device 106 for transferring thesheet 101 transferred by the primary paper feed device 103 to a portionbetween a printing drum 104 and a press roller 105 at predeterminedtiming.

The primary paper feed device 103 includes a scraper roller 107press-contacted with the uppermost sheet 101 on the paper feed tray 102,a stripper plate 108 arranged in the vicinity of the downstream side ofthe scraper roller 107, and a pickup roller 109 substantiallypress-contacted with the stripper plate 108. The scraper roller 107 andthe pickup roller 109 are driven to rotate in the same direction byprimary driving device (not shown). The secondary paper feed device 106includes a pair of secondary paper feed rollers 110 arranged downstreamof the primary paper feed device 103 in a sheet transfer direction, anda pair of guide members 112 and 113 providing a transfer path 111between the members 112 and 113 in the vicinity of the paired secondarypaper feed rollers 110. The paired secondary paper feed rollers 110 aredriven to rotate by secondary driving device (not shown). The upperguide member 112 guides only the neighborhood of the secondary paperfeed roller 110 and the upstream side of the upper guide member 112 inthe sheet transfer direction is formed as an inclined section 112 adirected upward.

With the above-described constitution, when the scraper roller 107 andthe pickup roller 109 are rotated, the uppermost sheet 101 on the paperfeed tray 102 is applied with a transfer force and thereby transferred,whereby a sheet 101 under the uppermost sheet 101 is also transferred byfrictional resistance between the sheet 101 and the uppermost sheet 101.If the sheet 101 is transferred to a position at which the tip end ofthe sheet 101 enters between the stripper plate 108 and the pickuproller 109, a plurality of sheets 101 are dealt with the stripper plate108 and the transfer of sheets 101 other than the uppermost sheet 101 isstopped at the stripper plate 108. At the same time, only the uppermostsheet 101 is transferred to a downstream side. When the sheet 101 thustransferred is guided by the guide member 113 and transferred to aposition near the paired secondary paper feed rollers 110, the sheet 101enters the transfer path 111 between the paired guide members 112 and113. If the sheet 101 passes this transfer path 111, the tip end of thesheet 101 is introduced to the portion between the paired secondarypaper feed rollers 110 and, as shown in FIG. 2, the transfer of thesheet 101 is stopped in a state in which the tip end side of the sheet101 is slightly bent. Next, the paired secondary paper feed rollers 110are rotated synchronously with the rotation of the printing drum 104. Ifthe paired secondary paper feed rollers 110 are rotated, the sheet 101which has been transferred to the portion between the paired secondarypaper rollers 110 is applied with a transfer force and therebytransferred to the portion between the printing drum 104 and the pressroller 105 at predetermined timing. The sheet 101 is transferred to theportion between the printing drum 104 and the press roller 105 whilebeing press-contacted with the portion and printing is conducted to thesheet 101 in this press-contact transfer course.

Meanwhile, the paired guide members 112 and 113 introducing the tip endof the sheet 101 transferred by the primary paper feed device 103 to theportion between the paired secondary paper feed rollers 110 are set tohave a constant distance h therebetween in the proposed paper feedapparatus.

However, if the distance h between the paired guide members 112 and 113is set to be wide enough to allow a thick sheet to pass through thetransfer path with a margin left, correction of sheet corrugation cannotbe expected to be exerted to a thin sheet, a sheet with less flexibilityor a largely corrugated sheet after being left for a while. As a result,the problem that the printed sheet 101 is wrinkled occurs. That is, asshown in FIG. 3, if the sheet 101 has a corrugated portion “a” andpasses between the paired secondary paper feed rollers 110 withoutcorrecting this corrugated portion “a”, then the corrugated portion “a”is crushed between the paired secondary paper feed rollers 110 and thesheet 101 has wrinkles “b” as shown in FIG. 4.

On the other hand, if the distance h between the paired guide members112 and 113 is set to allow a thick sheet (including an envelope and thelike) to pass between the paired guide members 112 and 113 narrowly,correction of sheet corrugation is expected to be exerted to a thinsheet, a sheet with less flexibility or a sheet corrugated after beingleft for a while. However, the problem that the thick sheet tends toclog occurs.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems. It is, therefore, an object of the present invention toprovide a paper feed apparatus which does not cause paper clogging whenthick sheets are used and which does not generate wrinkles on sheets ifthin sheets are used.

The first aspect of the invention provides a paper feed apparatuscomprising: a paper feed tray for mounting a plurality of sheets in astacked state; primary paper feed device for sequentially transferringonly the uppermost sheet out of the sheets on the paper feed tray; apair of secondary paper feed rollers arranged downstream of the primarypaper feed device in a sheet transfer direction, and a pair of guidemembers providing a transfer path between the pair of guide members nearthe pair of secondary paper feed rollers; secondary paper feed devicefor introducing tip ends of the sheets transferred by the primary paperfeed device by using the pair of guide members to a portion between thepaired secondary paper feed rollers, and for transferring the sheetsintroduced to the portion between the pair of secondary paper feedrollers to a transport downstream side according to rotation of the pairof secondary paper feed rollers; and guide distance adjustment devicefor making a distance between the pair of guide members variable,wherein the guide distance adjustment device comprises an operationmember operated by a user, and the guide distance adjustment devicemakes the distance between the pair of guide members variable byoperating the operation member.

According to the first aspect of the invention, if the sheets are thick,the distance between a pair of guide members is set wide, therebytransferring the sheets to the transfer path between the paired guidemembers with a margin left. If the sheets are thin sheets, sheets withless flexibility or the like, the distance between the paired guidemembers is set narrow. By doing so, the sheets are subjected tocorrection of sheet corrugation at the time of passing through thetransfer path between the paired guide members and then introduced tothe portion between a pair of secondary paper feed rollers. Due to this,it is possible to prevent wrinkles derived from the pressurization ofcorrugated portions by the paired secondary paper feed rollers.Furthermore, a user can freely, arbitrarily change the distance betweenthe paired guide members in light of the thickness of the sheets to beused or the like.

The second aspect of the invention provides a paper feed apparatuscomprising: a paper feed tray for mounting a plurality of sheets in astacked state; primary paper feed device for sequentially transferringonly the uppermost sheet out of the sheets on the paper feed tray; apair of secondary paper feed rollers arranged downstream of the primarypaper feed device in a sheet transfer direction, and a pair of guidemembers providing a transfer path between the pair of guide members nearthe pair of secondary paper feed rollers; secondary paper feed devicefor introducing tip ends of the sheets transferred by the primary paperfeed device by using the pair of guide members to a portion between thepaired secondary paper feed rollers, and for transferring the sheetsintroduced to the portion between the pair of secondary paper feedrollers to a transport downstream side according to rotation of the pairof secondary paper feed rollers; and guide distance adjustment devicefor making a distance between the pair of guide members variable,wherein the guide distance adjustment device comprises a rotatablyprovided eccentric cam, and the guide distance adjustment device makesthe distance between the pair of guide members variable according to arotation position of the eccentric cam.

According to the second aspect of the invention, the distance betweenthe paired guide members can be changed by eccentric cams eithercontinuously or by stages.

The third aspect of the invention provides a paper feed apparatusaccording to the second aspect of the invention, wherein the primarypaper feed device comprises a primary paper feed roller, the primarypaper feed roller comprises a paper feed pressure variable operationmember for changing paper feed pressure for pressing the sheets in thestacked state on the paper feed tray, and the primary paper feed rollerdrives the guide distance adjustment device in association with thepaper feed pressure variable member, so that the distance between thepair of guide members is made variable.

According to the third aspect of the invention, if the sheets are thick,a paper feed pressure variable operation member is operated to set paperfeed pressure high. If the sheets are thin, the paper feed pressurevariable operation member is operated to set paper feed pressure low. Bydoing so, the distance between the paired guide members is made variablein association with this paper feed pressure variable operation member.

The fourth aspect of the invention provides a paper feed apparatusaccording to the second aspect of the invention, wherein the paper feedapparatus is constituted to detect a slide ratio of the sheets whentransferring the sheets to the secondary paper feed device by theprimary paper feed mans, to drive the guide distance adjustment deviceaccording to the detected slide ratio and to thereby make the distancebetween the pair of guide members variable.

According to the fourth aspect of the invention, if the sheets arethick, a high slide ratio is detected and if the sheets are thin, a lowslide ratio is detected. The distance between the paired guide membersis made variable in association with this slide ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevational view of a proposed paper feedapparatus;

FIG. 2 is a side elevational view of the secondary paper feed device ofthe proposed paper feed apparatus;

FIG. 3 is a perspective view of the proposed paper feed apparatus andshowing a state before a print sheet having a corrugated portion passessecondary paper feed rollers;

FIG. 4 is a perspective view of the proposed paper feed apparatus andshowing a state in which the corrugated portion is crushed by thesecondary paper feed rollers and the sheet is wrinkled;

FIG. 5 is a schematic side elevational view of a paper feed apparatusaccording to the present invention;

FIG. 6A is a perspective view of secondary paper feed device of thepaper feed apparatus according to the present invention;

FIG. 6B is a side elevational view of the secondary paper feed deviceaccording to the present invention and showing that the distance betweena pair of guide members is a small distance h1;

FIG. 6C is a side elevational view of the secondary paper feed deviceaccording to the present invention and showing that the distance betweena pair of guide members is a normal distance h2;

FIG. 6D is a side elevational view of the secondary paper feed deviceaccording to the present invention and showing that the distance betweena pair of guide members is a large distance h3;

FIG. 7 is a perspective view of paper feed pressure adjustment deviceaccording to the present invention;

FIG. 8A is a perspective view of the paper feed pressure adjustmentdevice according to the present invention and showing the arrangement ofan upper limit sensor and a paper feed pressure control arm if the paperfeed pressure is low (i.e., if an ordinary sheet is used); and

FIG. 8B is a perspective view of the paper feed pressure adjustmentdevice according to the present invention and showing the arrangement ofthe upper limit sensor and the paper feed pressure control arm if thepaper feed pressure is high (i.e., if a thick sheet is used).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention will be describedwith reference to the drawings.

1. First Embodiment

As shown in FIG. 5, a paper feed apparatus 1 includes a paper feed tray2 mounting many sheets or print sheets P in a stacked state, primarypaper feed device 3 for transferring only the uppermost print sheet P onthe paper feed tray 2, and secondary paper feed device 4 fortransferring the print sheet P transferred by the primary paper feeddevice 3 to a portion between a printing drum (not shown) and a pressroller (not shown) at predetermined timing.

The paper feed tray 2 is constituted by elevator ascending/descendingdevice (not shown) so as to be vertically movable. The lower positionand the upper position of the paper feed tray 2 are detected by a lowerlimit sensor (not shown) and an upper limit sensor 5, respectively. Thelower position is a position for supplying the print sheets P or thelike to the paper feed tray 2 or replacing the print sheets P or thelike. The upper position is a position for transferring the print sheetsP on the paper feed tray 2. The position of the uppermost stacked printsheet P is set by pressing the upper limit sensor 5 through a scraperroller 7 to be described later. If print sheets P are fed onto the paperfeed tray 2, the position of the scraper roller 7 is lowered and theupper limit sensor 5 is turned off. Then, the paper feed tray 2continues to rise until the upper limit sensor 5 is turned on, wherebythe uppermost print sheet P is set at a position at which the uppermostprint sheet P always presses the scraper roller 7.

The primary paper feed device 3 includes the scraper roller 7 forserving as a primary paper feed roller which is press-contacted with theuppermost print sheet P if the paper feed tray 2 is located at the upperposition, a stripper plate 8 arranged in the vicinity of the downstreamside of the scraper roller 7, and a pickup roller 9 substantiallypress-contacted with the stripper plate 8. The scraper roller 7 ispress-contacted with the uppermost print sheet P on the paper feed tray2. During the transfer of the print sheets P, paper feed pressure isgenerated by the press-contact between the scraper roller and theuppermost print sheet P. This paper feed pressure can be varied by paperfeed pressure adjustment device 6 (see FIG. 7). The detailedconstitution of the paper feed pressure adjustment device 6 will bedescribed later.

The rotary shaft 7 a of the scraper roller 7 and the rotary shaft 9 a ofthe pickup roller 9 are rotatably supported by a roll support frame 25.The roll support frame 25 is supported by a paper feed apparatus mainbody so as to be rockable on a scraper roller 7 side. If the scraperroller 7 and the pickup roller 9 are not pressed by the print sheets Pon the paper feed tray 2, the scraper roller 7 and the pickup roller 9are slightly lowered. If pressed by the print sheets P on the paper feedtray 2, the scraper roller 7 and the pickup roller 9 are raised. Thescraper roller 7 and the pickup roller 9 are driven to rotate in thesame direction by primary driving device (not shown) in cooperation witheach other. One-way clutches (not shown) are interposed between thescraper roller 7 and the rotary shaft 7 a thereof and between the pickuproller 9 and the rotary shaft 9 a thereof, respectively. In FIG. 5, theone-way clutches transmit the clockwise rotation of the shafts 7 a andthe clockwise rotation of the shaft 9 a to the scraper roller 7 and thepickup roller 9, respectively, while not transmitting the oppositerotation thereof.

The secondary paper feed device 4 includes a pair of secondary paperfeed rollers 10 arranged downstream of the primary paper feed device 3in the sheet transfer direction, and a pair of guide device 12 and 13providing a transfer path 11 therebetween in the vicinity of the pairedsecondary paper feed rollers 10. The paired secondary paper feed rollers10 are driven to rotate by secondary driving device (not shown). Theupper guide member 12 guides only the neighborhood of the secondarypaper feed roller 10 and the upstream side of the upper guide member 12in the sheet transfer direction is formed as an inclined section 12 adirected upward. The lower guide member 13, which is arranged to extendfrom the paper feed tray 2 side to the position near the secondary paperfeed roller 10, guides the transfer of the print sheets P. The distanceh between the paired guide members 12 and 13 is made variable by guidedistance adjustment device 14 to be described later. A sheet-in sensor Sis provided while setting a position near the portion between the pairedsecondary paper feed rollers 10 as a detection position. If thissheet-in sensor S detects the tip end of the print sheet P, the drivingof the primary paper feed driving device (not shown) is controlled to bestopped after the passage of a predetermined time.

As shown in FIG. 6A, the guide distance adjustment device 14 includes anoperation member 20 arranged at a position at which a user can carry outa rotation operation. A pair of right and left eccentric cams 22 arefixed to the support shaft 21 of the operation member 20. Each of thepaired right and left eccentric cams 22 has a substantially rectangularparallelepiped shape and the distances from the center of the supportshaft 21 to respective sides of a cross-section of the rectangularparallelepiped differ. The upper guide member 12 is arranged below theeccentric cams 22. The upper guide member 12 is supported to bevertically movable. Compressive spring 23 are provided on both right andleft ends between the upper guide member 12 and the lower guide member13, respectively. Spring forces of the compressive springs 23 urge theupper guide member 12 toward the eccentric cams 22 side. The upper guidemember 12 moves vertically to follow up the surfaces of lower sides ofthe eccentric cams 22, whereby the distance h between the paired guidemembers 12 and 13 is variable to, for example, a small distance h1, anordinary distance h2 or a large distance h3 as shown in FIGS. 6B to 6D.

The paper feed pressure adjustment device 6 includes a paper feedpressure variable operation member 26 (shown in FIG. 7) rotatablysupported on the roller support frame 25 and operated by a user, and apaper feed pressure control arm 29 rock ably supported on the uppersurface of the roll support frame 25 through a support pin 27 (shown inFIGS. 8A and 8B) and moved against the spring force of a spring 28 bythe operation of the paper feed pressure variable operation member 26.By setting the upper surface of this paper feed pressure control arm 29or the upper surface of the roll support frame 25 as the detectionposition of the upper sensor 5, the paper feed pressure becomesvariable.

As indicated by a two-dot chain line shown in FIG. 7, the upper positionat which the paper feed pressure variable operation member 26 is locatedis a low paper feed pressure (that is, ordinary sheet) position. At thisposition, as indicated by solid lines shown in FIGS. 8A and 5, the uppersensor 5 is turned on while a force with which the sheets P press thescraper roller 7 is low and the upper limit sensor 5 uses the uppersurface of the paper feed pressure control arm 29 as a detectionposition, thereby setting the paper feed pressure to be low. Asindicated by a solid line shown in FIG. 7, the lower position at whichthe paper feed pressure variable operation member 26 is located is ahigh paper feed pressure (that is, thick sheet) position. At thisposition, as shown in FIG. 8B, the upper limit sensor 5 is turned onafter the force with which the sheets P press the scraper roller 7intensifies so that the upper limit sensor 5 uses the upper surface ofthe roll support frame 25 as a detection position, thereby setting thepaper feed pressure to be high.

With the above-described constitution, when the scraper roller 7 and thepickup roller 9 are rotated, the uppermost print sheet P on the paperfeed tray 2 is applied with a transfer force and thereby transferred. Aprint sheet P or the like under the uppermost print sheet P is alsotransferred by frictional resistance between the print sheet P and theuppermost print sheet P. If the print sheets P are transferred to aposition at which the tip ends of the print sheets P enter the portionbetween the stripper plate 8 and the pickup roller 9, a plurality ofprint sheets P are dealt with the stripper plate 8. Then, while thetransfer of the print sheets P other than the uppermost print sheet P isstopped, only the uppermost print sheet P is transferred to thedownstream. The print sheet P thus transferred is guided by the lowerguide member 13. If the print sheet P is transferred near the pairedsecondary paper feed rollers 10, the print sheet P enters the transferpath 11 between the paired guide members 12 and 13. If the paper sheet Ppasses this transfer path 11, the tip end of the print sheet P isintroduced to a portion between the paired secondary paper feed rollers10 and detected by the sheet-in sensor S. After the passage of apredetermined time since this tip end is detected, the scraper roller 7and the pickup roller 9 are stopped to rotate. At this moment, the tipend of the print sheet P abuts the portion between the paired secondarypaper feed rollers 10 and the transfer of the print sheet P is stoppedin a state in which the tip end side of the print sheet P is slightlybent.

Next, the paired secondary paper feed rollers 10 are rotatedsynchronously with the rotation of the printing drum (not shown), andthe print sheet P, which has been transferred to the portion between thepaired secondary paper feed rollers 10, is applied with a transfer forceand thereby transferred to a portion between the printing drum (notshown) and the press roller (not shown) at predetermined timing. At thismoment, the scraper roller 7 and the pickup roller 9 are press-contactedwith the print sheet P. The scraper roller 7 and the pickup roller 9 runidle by device of the respective one-way clutches (not shown), therebyallowing the transfer of the print sheet P. The print sheet P istransferred between the printing drum (not shown) and the press roller(not shown) while being press-contacted with the printing drum and thepress roller, and printing is conducted to the print sheet P in thispress-contact and transfer process.

In the above-described operation, if the print sheets P to be used arethick, the user operates the operation member 20 to adjust the distancebetween the paired guide members 12 and 13 to be wide as shown in FIG.6D. By doing so, the print sheets P are transferred to the transfer path11 between the paired guide members 12 and 13 with a margin left. If theprint sheets P to be used are thin paper, paper with less flexibility orthe like, the distance of the paired guide members 12 and 13 is adjustedto be narrow as shown in FIG. 6B. By doing so, if passing through thetransfer path 11 between the paired guide members 12 and 13, the printsheets P are subjected to correction of sheet corrugation and thecorrugation-corrected print sheets P are introduced to the portionbetween the paired secondary guide rollers 10. It is, therefore,possible to prevent the generation of wrinkles of the print sheets Pderived from the pressurization of corrugated portions by the pairedsecondary paper feed rollers 10. Accordingly, it is possible to preventpaper clogging if thick sheets are used as the print sheets P and toprevent sheets from being wrinkled if the sheets are thin.

If many print sheets P are transferred by the primary paper feed device3 once and the print sheets P clog between the paired guide device 12and 13, it is difficult for the user to remove the clogging sheets bythe user's hands in the proposed paper feed apparatus. According to thepresent invention, by contrast with the proposed paper feed apparatus,it is possible to easily widen the distance between the paired guidemembers 12 and 13 and, therefore, possible for the user to remove theclogging sheets by the user's hands.

The guide distance adjustment device 14 has the operation member 20which the user can operate. Since the guide distance adjustment device14 is constituted to make the distance between the paired guide members12 and 13 variable by the operation of this operation member 20, it ispossible for the user to freely, arbitrarily change the distance betweenthe paired guide members 12 and 13 in light of the thickness of sheetsto be used.

The guide distance adjustment device 14 has the eccentric cams 22 whichare rotatably provided. Since the guide distance adjustment device 14 isconstituted to make the distance between the paired guide members 12 and13 variable according to the rotating positions of the cams 22, it ispossible for the user to easily change the distance between the pairedguide members 12 and 13 by device of the eccentric cams 22 eithercontinuously or by stages. In this embodiment, the distance between thepaired guide members 12 and 13 are variable by stages. If the distancebetween the outer peripheral surface of each eccentric cam 22 and therotation center of the cam 22 is set to be gradually variable, thedistance between the paired guide members 12 and 13 can be variedcontinuously.

2. Second Embodiment

Hereinafter, the second embodiment of the present invention will bedescribed with reference to FIGS. 5 to 8B. In the first embodiment, thepaper feed apparatus is constituted to make the distance between thepaired guide members 12 and 13 variable by the operation of theoperation member 20. In the second embodiment, the operation member 20for guide distance adjustment device 14 is not provided, and theeccentric cams 22 are rotated and moved in association with theoperation of the paper feed pressure variable operation member 26,whereby the distance between a pair of guide members 12 and 13 are madevariable. Specifically, when the paper feed pressure variable operationmember 26 is located at the upper position (that is, low paper feedpressure (or ordinary sheet) position) indicated by the two-dot chainline shown in FIG. 7, the paired guide members 12 and 13 are moved topositions as shown in FIG. 6B or 6C, thereby changing the distancebetween the paired guide members 12 and 13. When the paper feed pressurevariable operation member 26 is located at the lower position (that is,high paper feed pressure (or thick sheet) position) indicated by thesolid line shown in FIG. 7, the paired guide members 12 and 13 are movedto positions as shown in FIG. 6D, thereby changing the distance betweenthe paired guide members 12 and 13. The other constitution is the sameas that of the first embodiment.

In the second embodiment, if print sheets P to be used are thick, theuser operates the paper feed pressure variable operation member 26 so asto be located at the lower position. By doing so, a value of the paperfeed pressure is set high to ensure the transfer of the print sheets P.The distance between the paired guide members 12 and 13 is set wide asshown in FIG. 6D, and the print sheets P are transferred to the transferpath between the paired guide members 12 and 13 with a margin left. Ifthe print sheets P to be used are thin sheets, sheets with lessflexibility or the like, the user operates the paper feed pressurevariable operation member 26 so to be located at the upper position. Bydoing so, a value of the paper feed pressure is set low to ensure thetransfer of the print sheets P. The distance between the paired guidemembers 12 and 13 is set narrow as shown in FIG. 6B or 6C. Accordingly,the print sheets P are subjected to correction of sheet corrugation atthe time of passing through the transfer path 11 between the pairedguide members 12 and 13, and introduced to the portion between a pair ofsecondary paper feed rollers 10. As a result, it is possible to preventthe generation of wrinkles of the print sheets P derived from thepressurization of corrugated portions by the paired secondary paper feedrollers 10.

As described above, the paper feed apparatus in the second embodimentcan prevent paper clogging if the print sheets P to be used are thicksheets, and prevent the print sheets P from being wrinkled if the sheetsP are thin sheets. If the user operates the paper feed pressure variableoperation member 26, it is not necessary to operate the guide distanceadjustment device 14.

In this case, the displacement positions of the paper feed pressurevariable operation member 26 may be three or more, and the distancebetween the paired guide members 12 and 13 may be made adjustable tothree stages in association with the displacement positions of themember 26.

3. Third Embodiment

Hereinafter, the third embodiment of the present invention will bedescribed with reference to FIGS. 5 to 8B. In the first embodiment, thepaper feed apparatus is constituted to make the distance between thepaired guide members 12 and 13 variable by the operation of theoperation member 20. In the third embodiment, however, the operationmember 20 for guide distance adjustment device 6 is not provided thesame as the case of the second embodiment. In the third embodiment, thepaper feed apparatus is constituted to detect the slip ratio of printsheets P at the time of transferring the print sheets P to the secondarypaper feed device 4 by the primary paper feed device 3, so as to rotateand move the eccentric cams 22 according to the slip ratio thus detectedand so as to make the distance between a pair of guide members 12 and 13variable. Specifically, a transfer time, that is, time between time atwhich the scraper roller 7 and the pickup roller 9 start to transfer theprint sheet P and time at which a sheet-in sensor S detects the tip endof the print sheet P, is detected, so that a slide ratio is calculatedbased on this transfer time. As the print sheet P is thicker, thetransfer time is longer and the slide ratio is higher. As the printsheet P is thinner, the transfer time is shorter and the slide ratio islower. Accordingly, if the transfer time is equal to or shorter than apredetermined time, the paired guide members 12 and 13 are moved topositions as shown in FIG. 6B or 6C. If the transfer time is equal to orlonger than the predetermined time, the paired guide members 12 and 13are moved to a position as shown in FIG. 6D. The other constitution ofthis embodiment is the same as that of the first embodiment.

In the third embodiment, if print sheets P to be used are thick, thedistance between the paired guide members 12 and 13 is set wide as shownin FIG. 6D and the print sheets P are transferred to a transfer path 11between the paired guide members 12 and 13 with a margin left. If theprint sheets P to be used are thin sheets, sheets with less flexibilityor the like, the distance between the paired guide members 12 and 13 isset narrow as shown in FIG. 6B or 6C. Accordingly, the print sheets Pare subjected to correction of sheet corrugation at the time of passingthrough the transfer path 11 between the paired guide members 12 and 13,and introduced to the portion between a pair of secondary paper feedrollers 10. It is, therefore, possible to prevent the generation ofwrinkles of the print sheets P derived from the pressurization ofcorrugated portions by the paired secondary paper feed rollers 10.

As described above, the paper feed apparatus in the third embodiment canprevent paper clogging if thick sheets are used as the print sheets P,and prevent the print sheets P from being wrinkled if the sheets arethin. It is not necessary for the user to operate the guide distanceadjustment device 6. Furthermore, it is not necessary for the user tooperate the paper feed pressure variable operation member 26 as shown inthe second embodiment. In this case, the distance between the pairedguide members 12 and 13 may be adjustable to have three or more stagesin association with the slide ratio.

In the above described each embodiment, the primary paper feed device 3is constituted to include the scraper roller 7, the pickup roller 9 andthe stripper plate 8. The constitution of the primary paper feed device3 is freely set as long as the device can transfer the print sheets P onthe paper feed tray 2 one by one. The distance between the paired guidemembers 12 and 13 is made variable by using the eccentric cams 22. Thedistance between the paired guide members 12 and 13 may be variableeither by stages or continuously. The present invention is applied tothe paper feed apparatus 1 of a stencil printing machine. The presentinvention is also applied not only to a printing machine other than thestencil printing machine but also to a copying machine or the like. Thepresent invention is applicable to an arbitrary machine as long as themachine includes a paper feed apparatus sequentially transferring onlyan uppermost sheet out of a plurality of sheets mounted in a stackedstate on a paper feed tray 2 at predetermined timing.

What is claimed is:
 1. A paper feed apparatus comprising: a paper feedtray for mounting a plurality of sheets in a stacked state; primarypaper feed means for sequentially transferring only the uppermost sheetout of the sheets on the paper feed tray; a pair of secondary paper feedrollers arranged downstream of the primary paper feed means in a sheettransfer direction, and a pair of guide members providing a transferpath between the pair of guide members near the pair of secondary paperfeed rollers; secondary paper feed means for introducing tip ends of thesheets transferred by the primary paper feed means by using the pair ofguide members to a portion between the paired secondary paper feedrollers, and for transferring the sheets introduced to the portionbetween the pair of secondary paper feed rollers to a transportdownstream side according to rotation of the pair of secondary paperfeed rollers; and guide distance adjustment means for making a distancebetween the pair of guide members variable, wherein the guide distanceadjustment means comprises an operation member, and the guide distanceadjustment means makes the distance between the pair of guide membersvariable by operating the operation member.
 2. A paper feed apparatuscomprising: a paper feed tray for mounting a plurality of sheets in astacked state; primary paper feed means for sequentially transferringonly the uppermost sheet out of the sheets on the paper feed tray; apair of secondary paper feed rollers arranged downstream of the primarypaper feed means in a sheet transfer direction, and a pair of guidemembers providing a transfer path between the pair of guide members nearthe pair of secondary paper feed rollers; secondary paper feed means forintroducing tip ends of the sheets transferred by the primary paper feedmeans by using the pair of guide members to a portion between the pairedsecondary paper feed rollers, and for transferring the sheets introducedto the portion between the pair of secondary paper feed rollers to atransport downstream side according to rotation of the pair of secondarypaper feed rollers; and guide distance adjustment means for making adistance between the pair of guide members variable, wherein the guidedistance adjustment means comprises a rotatably provided eccentric cam,and the guide distance adjustment means makes the distance between thepair of guide members variable according to a rotation position of theeccentric cam.
 3. A paper feed apparatus according to claim 2, whereinthe paper feed apparatus is constituted to detect a slide ratio of thesheets when transferring the sheets to the secondary paper feed means bythe primary paper feed mans, to drive the guide distance adjustmentmeans according to the detected slide ratio and to thereby make thedistance between the pair of guide members variable.